Forced suction and exhaust type gas burner apparatus

ABSTRACT

A forced suction and exhaust type gas burner apparatus comprising a gas burner unit and a fan motor for forcibly sucking air into said burner unit from the outdoor and exhausting the combustion gases from said burner unit to the outdoor so as to prevent air pollution in the room in which the burner unit is disposed and thereby to provide a sanitary environment inside the room. The gas burner apparatus is so designed that a stable combustion can be obtained and the suction and exhaust can be achieved in a rational manner, irrespective of variations in the flow resistances of suction and exhaust passages, the type of a gas used and line voltage and of differences in local frequency.

United States Patent [1 1 Kawabata et al.

[ 1 FORCED SUCTION AND EXHAUST TYPE GAS BURNER APPARATUS [75] Inventors: Norio Kawabata, Yamatokoriyama;

Nobuyuki Kimpara, Nara; Manabu Takata, Yamatokoriyama, all of Japan [73] Assignee: Matsushita Electric Industrial Co.,

Ltd., Osaka, Japan 22 Filed: 01:1.26, 1971 21 App1.No.: 192,281

[ Oct. 16, 1973 FOREIGN PATENTS OR APPLICATIONS 1,220,033 l/1971 Great Britain 126/85 B Primary Examiner-Edward G. Favors AttorneyRichard K. Stevens et al.

[5 7] I ABSTRACT A forced suction and exhaust type gas burner apparatus comprising a gas burner unit and a fan motor for forcibly sucking air into said burner unit from the outdoor and exhausting the combustion gases from said burner unit to the outdoor so as to prevent air pollution in the room in which the burner unit is disposed and thereby to provide a sanitary environment inside the room. The gas burner apparatus is so designed that a stable combustion can be obtained and the suction and exhaust can be achieved in a rational manner, itrespective of variations in the flow resistances of suction and exhaust passages, the type of a gas used and line voltage and of differences in local frequency.

3 Claims, 8 Drawing Figures PATENTEBnm 15 1913 SHEETIOF 6 PAIENIEnum 15 Ian 3.765823 sum 2 OF 6 PATENTEDUCT 15 1975 3.765823 SHEET 30$ 6 minnow 1s m 3.765323 saw a or 6 FIG. 5

PATENTEDHBT 16 I975 3.765323 sums 0F 6 EXCESS AIR R4770 FLOW 5455 OF A/RO FORCED SUCTION AND EXHAUST TYPE GAS BURNER APPARATUS This invention relates to a forced suction and exhaust gas burner apparatus which comprises a fan motor for forcibly causing suction and exhaust necessary for the combustion and in which the characteristic of said fan motor representing the relationship between the frictional loss in suction and exhaust ducts caused by air flow generated by the fan motor and the flow rate of air (hereinafter referred to as P-Q characteristic) is set in relation with the frictional loss caused by a burner unit or the suction and exhaust passages and the excess air ratio during combustion, whereby an excellent combustion efficiency can be obtained irrespective of the equivalent length (including curved portions) and diameter of the suction and exhaust passages, the type of a gas used, and the voltage and frequency supplied to the fan motor.

Conventional gas burner apparatus of the type in which air is sucked from and the combustion gases are exhausted to the outdoor for the purpose of preventing air pollution inside a room in which the apparatus is disposed, include a balanced flue type gas burner apparatus. In this type of gas burner apparatus, the fresh outdoor air is sucked into a burner unit, not by using a fan but by taking advantage of the draft of the combustion gases thereby maintaining the balance between the exhaust and the suction. However, in this type of apparatus the combustion efficiency is liable to be influenced by the atmospheric conditions. For instance, in a windy day the exhaust of the combustion gases is impaired and as a result, the balance between the exhaust and the suction is disturbed, resulting in an incomplete combustion.

On the other hand, as a burner apparatus which is free of the above-described disadvantage of the balanced flue type burner apparatus, there has been proposed a so-called forced suction and exhaust type gas burner apparatus in which suction and exhaust are forcibly caused by a fan motor. In this type of burner apparatus, however, it has been necessary to set the P-Q characteristic of the fan motor from time to time in accordance with various conditions of a burner unit, a suction-exhaust unit,.etc., which has frequently rendered the installation procedures of the apparatus cumbersome. More specifically, in this type of burner apparatus the combustion state is varied mainly by (I) the flow rate of air which changes incident to a change in the frictional loss of air in accordance with the length of the suction and exhaust passages (including the passages in a burner unit, suction and exhaust ducts and a suction-exhaust unit), (II) the quantity of air necessary for combustion which varies depending upon the type of gas used and (III) the flow rate of air generated by the fan motor which is varied by variations in line voltage and differences in local frequency.

With reference first to the flow rate of air which varies incident to a change in the length of the suction and exhaust passages, mentioned in (I) above, the frictional loss becomes greater as the length of the suction and exhaust passages becomes longer and, with the capacity of the fan motor being constant, the increasing frictional loss finally adversely affects the states of suction and exhaust, causing a degradation of the combustion efficiency. Therefore, in the conventional apparatus it has been necessary to set the P-Q characteristic of the fan motor according to the particular length of the suction and exhaust passages. However, such a measure has been unsatisfactory not only in that it makes the installation procedures of the apparatus cumbersome, but also in that when the length of the suction and exhaust passages changes as a result of movement of the installation site of the apparatus, the fan motor in the apparatus can no longer be used. If the fan motor is continuously used in the apparatus in this case, an insufficient or conversely excess air will be supplied to the burner unit causing back-fire, yellow tips or lifting which degrades the combustion efficiency.

In other words, in the conventional burner apparatus of the type described the fan motor is adapted for use only under specific conditions.

With reference to the quantity of air which is variable depending upon the type of gas used, mentioned in (11) above, the quantity of air required for the combustion varies according to the type of gas used and, for instance, butane and natural gas call for a relatively large quantity of air and city gas calls for a relatively small quantity of air for combustion. Therefore, the characteristic of the fan motor used must be selected in accordance with the type of gas used, which is highly cumbersome.

v With reference to the voltage and frequency supplied to the fan motor, mentioned in (III) above, the flow rate of air generated by the fan motor is occasionally casually varied by variations in line voltage and differences in local frequency. In the conventional burner apparatus, the fan motor is not adaptable to the varying flow rate of air as stated above, so that such a variation in the flow rate of air obviously results in a degradation of the combustion efficiency.

The present invention has solved these problems by setting the P-Q characteristic of the fan motor in a rational manner.

An object .of the present invention is to'provide a forced suction and exhaust type gas burner apparatus which is capable of maintaining a stable state of combustion even when the length of suction and exhaust passages is changed or the type of fuel used is changed or further the voltage and frequency supplied to the fan motor is changed.

Another object of the invention is to provide a forced suction and exhaust type gas burner apparatus of the character described above, in which a fan motor is provided at the terminal end of the exhaust passage to generate a negative pressure in the suction and exhaust passages over substantially the entire length thereof, whereby a leakage of the combustion air before reaching a burner unitor a leakage of toxic exhaust gases into a room can be prevented even if the wall structure of said suction and exhaust passages is incomplete, and thereby the stability and safety of combustion can be further enhanced.

Still another object of the invention is to provide a forced suction and exhaust type gas burner apparatus of the character described above, in which the starting I end of the suction passage and the terminal end of the exhaust passage, extending outwardly through a wall of a house in which the apparatus is mounted, are arranged in superposed or telescoped relation to form a suction-exhaust unit, whereby the mounting operation of the suction and exhaust passages through the wall of the house is simplified.

Still another object of the invention is to provide a forced suction and exhaust type gas burner apparatus of the character described above, in which suction and exhaust ports of the burner unit are arranged in the same positional relation with the connecting ends of the suction-exhaust unit, so that said suction-exhaust unit may be directly connected with the burner unit when the burner unit is located close to the wall of the house, to provide for flexibility in the arrangement of the suction and exhaust passages.

Still another object of the invention is to provide a forced suction and exhaust type gas burner apparatus of the character described above, in which a wind breaker is provided in front of the exhaust opening of the suction-exhaust unit, whereby a degradation of the exhaust capacity otherwise caused by the external wind can be prevented and a stable operation of the fan motor can be ensured.

A further'object of the invention is to provide a forced suction and exhaust type gas burner apparatus of the character described above,'in which the fresh air passing in the suction passage is partially directed to v the fan motor, whereby overheating of said fan motor by the heat of the exhaust gases is prevented.

Other objects, features and advantages of the present invention will become apparent from the following detailed description when taken in conjunction with the accompanying drawings. In the drawings,

FIG. 1 is a front elevational view, partially broken away, of an embodiment of the forced suction and exhaust type gas burner apparatus according to the present invention;

FIG. 2 is an enlarged view of the burner unit shown in FIG. 1, with a portion thereof cut away to show the internal structure;

FIG. 3 is a vertical sectional view of the suctionexhaust unit;

FIG. 4 is a sectional view taken along the line 4-4 of FIG. 3; i

FIG. 5 is a top plan view of the burner unit shown in FIG. 1;

FIG. 6 is a front elevational view of the burner unit and the suction-exhaust unit connected directly with each other;

FIG. 7 is a vertical sectional view of another type of the suction-exhaust unit; and

FIG. 8 is a diagram graphically illustrating the P-Q characteristic of the fan motor, i.e. the relationship between the frictional loss of air in the suction and exhaust passages and the excess air ratio at the time of combustion.

An embodiment of the present invention will be described hereunder with reference to the accompanying drawings.

Referring to FIGS. 1 4, a burner unit generally indicated by numeral 1 includes an outer casing 2 and a water heating combustion part 3 housed in said outer casing 2. The combustion part 3 consists essentially of a main gas burner 4 and a heat exchanger 5 disposed above said main gas burner 4. Water is supplied to the heat exchanger 5 through a water pipe 6 and the hot water heated in the heat exchanger 5 is delivered to a desired place through a hot water pipe 7. A fuel gas is supplied to the gas burner 4 through a gas pipe 8. The gas pipe 8 is provided therein with a pilot safety device 9 utilizing a thermocouple and a water pressure responsive gas valve 10 operable in response to the water flow in the water pipe'6. The outer casing 1 is provided with a sight window 11 in the front wall, and a suction port 13 and an exhaust port 14 in the upper wall thereof, said suction port 13 communicating with the interior of the outer casing 1 and said exhaust port 14 communicating an exhaust portion of the combustion part 3. Reference numeral 12 designates an operating knob provided on the front wall of the outer casing 2.

A suction-exhaust unit generally indicated by numeral 15 comprises a suction duct 16 having a square cross section and an exhaust duct 17 disposed concentrically within the suction duct 16 and supported by said suction duct through a plurality of fittings 18. The suction-exhaust unit 15 extends outwardly through a waIl C of a house separating the indoor A and the outdoor B, and secured to said wall C by means of fittings 20, such as bolts and nuts, extending through a flange 9 formed around the suction duct 16. The outer end of the exhaust duct 17 projects further outwardly from the outer end of the suction duct 16 and flared outwardly to'constitute a partition member 21. Namely, the partition member 21 is located in such a position as to shut down the communication between an air inlet opening 16' of the suction duct 16 and an exhaust opening 17' of the exhaust duct 17, to prevent the combustion gases exhausted from the exhaust opening 17 from flowing into the air inlet opening 16. A dust cover 22 made from a perforated material such as a metal screen is provided at the outer end of the suction duct 16 extending forwardly from the peripheral edge thereof beyond the outer end of the exhaust duct 17. In the forward end of the dust cover 22 is provided a wind breaker 23 in opposed relation to the exhaust opening 17' of the exhaust duct 17, with its convexed surface facing said exhaust opening. A fan motor 24 has a nipple 25 connected to the suction side thereof and another nipple 26 connected to the discharge side thereof. The nipple 26 extends into the suction duct 16 and connected with the exhaust duct 17 within said suction duct. The peripheral wall and the end wall of the other end of the suction duct 16 inside the room are formed with a plurality of openings, and one of said openings has a nipple 27 of the same structure as the nipple 25 of the fan motor connected thereto, while another opening 30 is normally closed by a cover 31. Where the burner unit 1 is distant from the suctionexhaust unit 15 as shown in FIG. 1, the suction port 13 of the burner unit 1 and the nipple 27 of. the suction duct 16 are connected by a suction duct 28, and the exhaust port 14 and the nipple 25 of the fan motor 24 are connected by an exhaust duct 29. The suction duct 28 and the exhaust duct 29 are not arranged in telescoped relation as are the suction and exhaust ducts of the suctionexhaust unit 15, but are arranged separately from each other.

With the construction described above, when the fan motor 24 is set in motion and the combustion is commenced at the gas burner 4, the outdoor fresh air is sucked into the suction duct 16 from its air inlet opening 16 and flows into the outer casing 2 through the nipple 27, the suction duct 28 and the suction port 13 to be burned with the gas. At the same time, the combustion gases generated from the gas burner 4 flow into the exhaust duct 29 from the exhaust port 14 and after being pressurized by the fan motor 24, discharged to the outside through the exhaust duct 17 from its exhaust opening 17'.

As will be understood from the foregoing, during the operation of the apparatus, the suction duct 16, the suction duct 28, the interior of the outer casing 2 and the exhaust duct 29 are all located on the suction side of the fan motor 24. Namely, the substantially entire portion of the suction and exhaust passages, except for the exhaust duct 17 of the suction-exhaust unit is placed under negative pressure. Therefore, the air for combustion or the combustion gases will not be allowed to leak into the room even if the suction and exhaust passages are subjected to a minor damage. This is advantageous not only in keeping the indoor air sanitary but also in simplifying the sealing structure for the suction and exhaust passages.

In the construction described above, the suction duct 28 and the exhaust duct 29 are provided separately from each other. This is for the purpose of preventing the corrosion of the exhaust duct 29 by the condensed water and also facilitating the installation of said ducts. Explaining this in more detail, if the suction duct 28 and the exhaust duct 29 are arranged in telescoped relation, it will be necessary to make the space between the walls of these ducts uniform, which renders the bending of these ducts extremely difficult. Furthermore, the exhaust gases passing in the exhaust duct will be cooled by the air passing in the suction duct, and the water present therein is condensed and attached to the inner wall surface of the exhaust duct. The water thus attached to the inner surface of the exhaust duct reacts with sulfur or other compounds, causing a corrosion of said exhaust duct. The abovedescription will make explicit the advantage of providing the suction duct 28 and the exhaust duct 29 separately.

Since the suction-exhaust unit 15 has the suction duct 16 and the exhaust duct 17 arranged in telescoped relation as stated above, only one hole need be opened in the wall C for the installation of these ducts and thus the installation work of these ducts is extremely simplifled. On the other hand, such a construction of the suction-exhaust unit 15 may appear to be disadvantageous from the viewpoint of prevention of water condensation discussed above. However, in practice the length of the telescoped portions of the suction duct 16 and the exhaust duct 17 is short relative to the entire length of the exhaust passage and hence the exhaust gases passing in said portion of the exhaust duct 17 is not cooled to the condensation temperature of water.

As stated previously, the partition member 21 formed at the forward end of the exhaust duct 17 serves to prevent the exhaust gases, discharged from the exhaust opening 17 from flowing into the suction duct 16 and thereby to maintain satisfactory combustion at the gas burner 4. The wind breaker 23 is useful for the prevention of a lowering of the exhaust capacity caused by external wind.

The relative position of the nipple 25 of the fan motor 24 and the opening 30 formed in the peripheral wall of the inner end portion of the suction duct 16 and facing in the same direction as said nipple 25, is so selected as shown in FIG. 3. Namely, the nipple 25 and the opening 30 are spaced from each other by a distance l in one direction and a distance m in another direction perpendicular to said one direction. Similarly, the relative position of the suction port 13 and the exhaust port 14 of the burner unit lis so selected that they are spaced from each other by a distance I in one direction and a distance m in another direction perpendicular to said one direction, as shown in FIG. 5.

Therefore, when the burner unit is to be located close to the wall C, the nipple 25 of the fan motor 24 and the nipple 27 of the suction duct 16 can be connected with the exhaust port 14 and the suction port 13 of the burner unit 1 respectively, by removing the cover from the opening 30 shown in FIG. 3, connecting the nipple 27 to said opening, rotating the suction-exhaust unit 15 to direct the nipples 25 and 27 downwardly, rotating the burner unit 1 90 from the position shown in FIG. 1, with the backside thereof facing the wall C and then connecting the nipples 25 and 27 with the exhaust port 14 and the suction port 13 respectively. Namely, when the burner unit 1 is close to the wall C, the suction-exhaust unit 1 can be directly connected with the burner unit 1 as shown in FIG. 6. In FIG. 6, numeral 32 designates a cooling fan for cooling the fan motor 24.

In the operation of a general'gas burner, each gas used has its own theoretical air requirement for combustion. In the actual combustion, however, the air supplied is not entirely served for combustion but a part thereof is discharged along with the combustion gases. Therefore, in order to obtain a satisfactory combustion, a quantity of air larger than the theoretical requirement, i.e. the so-called excess air, must be supplied. The excess air ratio which is applicable to all gases, including butane gas, natural gas, etc. which call for a relatively large quantity of air and city gas and the like which call for a relatively small quantity of air, is generally in the range from 1.2 to 2.5. The value 1.2 is the lower limit of the excess air ratio, below which the combustion results in the generation of yellow tips and carbon monoxide, while the value 2.5 is the upper limit of the excess air ratio, above which the combustion results in lifting and degradation of the combustion eff1- ciency.

FIG. 8 is a graph illustrating the relationship between the excess air ratio and the frictional loss of air caused by the suction and exhaust passages with respect to the length of said passages, the axis of abscissa being scaled by the excess air ratio and the axis of ordinate by the frictional loss.

' In the graph, a curve a represents the frictional loss when the suction-exhaust unit 15 is directly connected with the burner unit 1 without using the suction duct 28 and the exhaust duct 29 shown in FIG. 6 or, in other words, when the length of the suction and exhaust passages is shortest, and in this case, the friction provided by the suction-exhaust unit 15 and the frictions provided by the outer casing 2 and the combustion part 3 are considered as the causes of the friction loss. Therefore, the friction loss is smallest in case of the curve a. Of course, the friction loss becomes larger as the excess air ratio increases. A curve b represents the friction loss when the suction duct '28 and the exhaust duct 29 are used as shown in FIG. 1, 'and as a matter of course, the friction loss is larger than in case of the curve a, by an amount corresponding to the length of the suction duct 28 and exhaust duct 29.

It has been revealed through the experiments conducted by the present inventors that the lengths of the suction duct 28 and exhaust duct 29 are each from 10 to 15 m at longest in view of the construction and size of a house. The length of 10 to 15 m mentioned above is the equivalent length including the lengths into which the increase of friction caused by the bent portions of any value within the allowable range all fall in the area between the curves and b.

Therefore, for'obtaining the desired characteristics of the fan motor, it is only necessary to set the PQ characteristic of the fan motor such that curves representing the P-Q characteristic intersect each of the curves representing the frictional loss in the suction and exhaust passages with respect to the excess air ratio when the total length of the suction and exhaust passages is minium and when the same is maximum within the area defined by the last mentioned curve and lines representing the excess air ratios of 1.2 and 2.5 respectively, irrespective of variations in line voltage or of differences in local frequency.

If the voltage and frequency supplied to the fan motor become highest, for example, 1 V, 60 Hz, then the P-Q characteristic of the fan motor will be represented by a curve 0 shown in FIG. 8, while if the voltage and frequency become lowest, for example, 85 V, 50 Hz, then the P-Q characteristic of the fan motor will be represented by a curve d shown in FIG. 8. Therefore, the P-Q characteristic of the fan motor will be always within the area between the curves 0 and d.

In the event when a specific gas is supplied in a certain quantity in every minute and burned within the burner unit, the quantity of air actually required per every minute is the product of the theoretical air requirement and the excess air ratio, and therefore, the excess, air ratio and the flow rate of air (m /min) are in proportional relation to each other. For this reason, the axis of abscissa of the graph of FIG. 8 is also scaled by the air flow rate.

The fan motor which has had its P-Q characteristic set in the manner described above is not only adapted for the combustion of any type of gas but also capable of supplying a quantity of air necessary for the combustion at all times, even when the length of the suction duct 28 and exhaust duct 29 changes. In addition, since the characteristics of the fan motor is always within the area between the curves 0 and d, a satisfactory combustion can be maintained even if the voltage and frequency of the power source change. I

Although in the graph of FIG. 8 the curve b is drawn based on the longest possible length of the suction duct 28 and exhaust duct 29, it may also be possible to classify the burner apparatus into a several types according to the length of the suction and exhaust passages and use fan motors of different characteristics adapted to the respective types of burner apparatus.

Referring to FIG. 7, there is shown another type of the suction-exhaust unit. In the suction-exhaust unit 33 shown, the suction and exhaust passages are put together into a unitary piece as well as the type described above but in such a manner as to prevent overheating of the fan motor.

Namely, the suction-exhaust unit 33 includes a guide duct 34 extending outwardly through the wall C of the house and secured to said wall by means of fittings 36 extending through a flange 35 formed around the outer surface thereof.

The interior of the guide duct 34 is divided by a partition plate 37 to form an exhaust guide passage 38 on the upper side and an air guide passage 39 on the lower side. A fan motor 40 comprises a centrifugal fan 41 and a motor 42 directly connected with each other by a rotary shaft 43 and a cooling fan 44 mounted on said rotary shaft 43 for cooling the motor 42. The fan 41 is housed in a casing 47 having an air inlet opening 45 and an air discharge opening 46 communicating with the exhaust guide passage 38. A by-pass passage 48 is formed at a portion of the partition wall 37 adjacent the air inlet opening 45 in the casing 47, communicating the negative pressure side of the exhaust guide passage 38 and the air guide passage 39 with each other, and a shutter 49 is provided to adjust the degree of opening of said by-pass passage 48, said shutter being operated externally by operating means'not shown. The ends of the exhaust guide passage 38 and the air guide passage 39, located inside the room, are provided with connecting ports 50 and 51 respectively, and the connecting port 50 is connected with the exhaust passage from the burner unit, while the connecting port 51 is connected with the suction passage of the same. With reference, for example, to the burner unit shown in FIG. 1, the exhaust duct 29 is connected with the connecting port 50 and the suction duct 28 with the connecting port 51. Numeral 52 designates a dust cover and 53 designates a wind breaker.

With the construction described above, when the fan motor 40 is set in motion, the combustion gases from the burner unit are sucked by the fan 41 and after passing through the exhaust guide passage 38, the air inlet opening 45, the casing 47 and the air discharge opening 46, discharged to the outside from the outerend opening of the exhaust guide passage 38. At the same time, the fresh air outside the house flows into the air guide passage 39 from its starting end while being sucked by the fan motor 40 and is supplied to the burner unit through the connecting port 51 and the air passage connected therewith.

' The partition wall 37 is formed with the by-pass passage 48 communicating the negative pressure side of the exhaust guide passage 38 with the air guide passage 39 as stated above. Therefore, during suction and exhaust, the fresh air passing in the air guide passage 39 partially flows into the exhaust guide passage via the by-pass passage 48 and cools the temperature of the exhaust gases at the terminal end of the exhaust guide passage 38. Therefore, the fan 41 will not be overheated although it is located adjacent the exhaust passage, and consequently, only a small quantity of heat transfers to the motor 42. When the overheating conditions for the motor 42 vary due to the change of season, the degree of opening of the by-pass passage 48 can be adjusted by means of the shutter 49.

It should be noted that the maximum degree of opening of the by-pass passage 48 must be set to a degree which does not change the P-Q characteristic of the fan motor defined between the curves 0 and d in the graph of FIG. 8.

Although the present invention has been described and illustrated herein in terms of a specific embodiment thereof, it should be obvious that many changes and modifications are possible within the scope not deviating from the spirit of the invention.

What is claimed is:

1. A forced suction and exhaust type gas burner apparatus comprising a suction-exhaust unit having a fan motor and a burner unit having a combustion part, in which a suction passage and an exhaust passage respectively extend from the combustion part to the outside of a house, the exhaust passage of the suction-exhaust unit and the discharge side of the fan motor provided exteriorly of said suction-exhaust unit being in communication with each other, and a connecting pipe provided at the suction part of the fan motor and a connecting pipe provided in the suction passage of the suction-exhaust unit are extended in the same direction, the positional relation of said two connecting pipes being the same as the positional relation of a suction port and an exhaust port which are provided at the upper surface of the burner unit such that the line connecting them with each other extends in a diagonal direction with respect to said upper surface, so that said suction-exhaust unit may be connected directly to the burner unit and the suction and exhaust ducts may be easily connected to the burner unit and suction-exhaust unit respectively without said two ducts interfering with each other, said apparatus being so designed that the suction-exhaust unit may be connected to the burner unit either directly or through a suction duct and an exhaust duct, and the interior of the burner unit and the interior of the suction duct and exhaust duct may be placed in a negative pressure condition, the ratio of excess air necessary for the combustion of gas being within the range of from 1.2 to 2.5, the P-Q characteristic of said fan motor being set such that curves representing said P-Q characteristic intersect each of the curves representing the frictional loss in said suction and exhaust passages with respect to the excess air ratio when the total length of said suction and exhaust passages is minimum and when the same is maximum within the area defined by said last mentioned curves and lines representing the excess air ratios of 1.2 and 2.5 respectively, irrespective of variations in line voltage or differences in local frequency.

2. A forced suction and exhaust type gas burner apparatus as defined in claim 1 in which a bypass passage leading from the suction passage is communicated with the suction side of the fan motor provided at the terminal end of the exhaust passage so as to lead a part of air in the suction passage to the fan motor through said bypass passage, to be mixed with the exhaust gas, whereby the exhaust gas temperature is lowered and overheating of said fan motor is prevented.

3. A forced suction and exhaust type gas burner apparatus as defined in claim 2, in which a shutter is provided to adjust the degree of opening of said by-pass 

1. A forced suction and exhaust type gas burner apparatus comprising a suction-exhaust unit having a fan motor and a burner unit having a combustion part, in which a suction passage and an exhaust passage respectively extend from the combustion part to the outside of a house, the exhaust passage of the suctionexhaust unit and the discharge side of the fan motor provided exteriorly of said suction-exhaust unit being in communication with each other, and a connecting pipe provided at the suction part of the fan motor and a connecting pipe provided in the suction passage of the suction-exhaust unit are extended in the same direction, the positional relation of said two connecting pipes being the same as the positional relation of a suction port and an exhaust port which are provided at the upper surface of the burner unit such that the line connecting them with each other extends in a diagonal direction with respect to said upper surface, so that said suction-exhaust unit may be connected directly to the burner unit and the suction and exhaust ducts may be easily connected to the burner unit and suction-exhaust unit respectively without said two ducts interfering with each other, said apparatus being so designed that the suction-exhaust unit may be connected to the burner unit either directly or through a suction duct and an exhaust duct, and the interior of the burner unit and the interior of the suction duct and exhaust duct may be placed in a negative pressure condition, the ratio of excess air necessary for the combustion of gas being within the range of from 1.2 to 2.5, the P-Q characteristic of said fan motor being set such that curves representing said P-Q characteristic intersect each of the curves representing the frictional loss in said suction and exhaust passages with respect to the excess air ratio when the total length of said suction and exhaust passages is minimum and when the same is maximum within the area defined by said last mentioned curves and lines representing the excess air ratios of 1.2 and 2.5 respectively, irrespective of variations in line voltage or differences in local frequency.
 2. A forced suction and exhaust type gas burner apparatus as defined in claim 1 in which a bypass passage leading from the suction passage is communicated with the suction side of the fan motor provided at the terminal end of the exhaust passage so as to lead a part of air in the suction passage to the fan motor through said bypass passage, to be mixed with the exhaust gas, whereby the exhaust gas temperature is lowered and overheating of said fan motor is prevented.
 3. A forced suction and exhaust type gas burner apparatus as defIned in claim 2, in which a shutter is provided to adjust the degree of opening of said by-pass passage. 